Stormwater Management Glossary
A reference of common terms used in stormwater engineering, urban drainage systems, and rooftop retention technologies. Written for engineers, planners, and infrastructure professionals.
B
- Blue Roof
A rooftop system designed to temporarily store rainwater and release it at a controlled rate. Blue roofs use flow-restriction devices or smart valves to manage drainage timing, reducing the volume and velocity of stormwater entering municipal infrastructure during peak rainfall events.
C
- Combined Sewer Overflow (CSO)
An event in which a combined sewer system—designed to carry both stormwater and sanitary sewage—exceeds its hydraulic capacity, causing untreated or partially treated wastewater to discharge into nearby water bodies. CSOs are a significant source of urban water pollution.
- Controlled Roof Drainage
A stormwater management approach in which rooftop drainage is regulated using valves, weirs, or smart devices to control the rate and timing of water release. This technique reduces peak runoff and aligns discharge with downstream infrastructure capacity.
D
- Detention Basin
A stormwater management facility designed to temporarily hold runoff during storm events and release it gradually over time. Detention basins reduce peak flow rates reaching downstream infrastructure but do not permanently store water.
- Distributed Stormwater Infrastructure
A decentralized approach to stormwater management in which multiple small-scale systems—such as rooftop retention devices, rain gardens, and permeable surfaces—are deployed across a watershed. This model reduces reliance on centralized pipe-and-basin systems by managing runoff at or near its source.
- Drain Flow Control
The regulation of water flow through building drainage systems using valves, orifices, or automated devices. Drain flow control is used to limit discharge rates from rooftops and impervious surfaces, helping align building-level outflow with municipal drainage capacity.
- Drainage Infrastructure
The engineered network of pipes, channels, culverts, basins, and outfalls that collects and conveys stormwater from urban surfaces to treatment facilities or receiving water bodies. Aging or undersized drainage infrastructure is a leading contributor to urban flooding.
G
- Green Roof
A rooftop surface partially or fully covered with vegetation and a growing medium, installed over a waterproof membrane. Green roofs absorb rainfall, reduce runoff volume through evapotranspiration, and provide thermal insulation. Their stormwater retention capacity depends on substrate depth and plant coverage.
H
- Hydraulic Capacity
The maximum volume of water that a drainage system, pipe, channel, or basin can convey or store under design conditions. When stormwater inflows exceed hydraulic capacity, the system surcharges, potentially causing surface flooding or structural damage.
- Hydrologic Modeling
The use of computational models to simulate rainfall-runoff processes, predict peak flows, and evaluate the performance of stormwater infrastructure under various storm scenarios. Common tools include EPA SWMM, HEC-HMS, and proprietary cloud-based platforms.
I
- Impervious Surface
Any surface that prevents or significantly reduces the infiltration of rainwater into the ground, such as rooftops, roads, parking lots, and sidewalks. High percentages of impervious cover increase runoff volume and peak flow rates, intensifying the load on downstream drainage systems.
O
- Overflow Protection
Safety mechanisms built into stormwater retention or drainage systems to prevent structural failure when water levels exceed design thresholds. Overflow protection typically includes emergency spillways, bypass channels, or automatic valve release triggered by depth sensors.
P
- Peak Runoff
The maximum rate of stormwater flow at a given point during or immediately after a rainfall event. Reducing peak runoff is a primary objective of stormwater management, as it determines whether downstream infrastructure can handle the load without flooding.
R
- Rainfall Intensity
The rate at which rain falls over a given period, typically measured in millimeters per hour (mm/h) or inches per hour (in/h). Rainfall intensity is a key input for sizing drainage infrastructure and modeling peak runoff volumes.
- Retention Basin
A stormwater facility designed to permanently hold a volume of water, capturing runoff and allowing it to infiltrate into the ground, evaporate, or be reused. Unlike detention basins, retention basins maintain a permanent pool and provide additional water quality treatment.
- Rooftop Retention Systems
Engineered systems installed on building rooftops to temporarily store rainwater and control its release into the drainage network. These systems may include smart valves, depth sensors, and cloud-connected controllers. Modern monitoring platforms such as SmartFlow provide real-time visibility into rooftop retention system performance across multiple buildings.
S
- Smart Stormwater Monitoring
The use of sensor networks, cloud platforms, and data analytics to track stormwater infrastructure performance in real time. Smart monitoring enables proactive management—including automated drain control and predictive alerting—rather than reactive response after flooding occurs. Platforms such as SmartFlow provide centralized dashboards for multi-site monitoring.
- SmartFlow Platform
A rooftop stormwater management platform that combines a smart roof device, cloud-based monitoring, and adaptive control logic to manage water retention and release in real time. SmartFlow enables building owners, facility managers, and municipalities to monitor drainage performance, reduce peak runoff, and coordinate stormwater management across multiple sites.
- Stormwater
Rainwater or snowmelt that flows over land surfaces rather than infiltrating into the ground. In urban areas, stormwater runs off impervious surfaces such as rooftops, roads, and parking lots, and must be managed through engineered drainage systems to prevent flooding and water quality degradation.
- Stormwater Detention
The temporary storage of stormwater runoff to reduce peak flow rates before releasing it into the downstream drainage system. Detention does not reduce the total volume of runoff—it redistributes it over time to prevent infrastructure overload during intense rainfall.
- Stormwater Retention
The capture and long-term storage of stormwater runoff, either through infiltration into the ground, evapotranspiration, or collection for reuse. Retention permanently removes a portion of runoff volume from the drainage system, reducing both peak flows and total discharge.
U
- Urban Flooding
Flooding that occurs in developed areas when stormwater runoff exceeds the capacity of drainage infrastructure. Urban flooding is intensified by impervious surfaces, aging pipe networks, and increasingly intense rainfall patterns driven by climate change.
- Urban Runoff
Stormwater that flows across urban surfaces—including streets, sidewalks, rooftops, and parking areas—collecting pollutants before entering storm drains, combined sewers, or water bodies. Urban runoff is a primary vector for non-point-source pollution and a leading cause of CSO events.
- Urban Watershed
The geographic area within or around a city from which all surface water drains to a common outlet, such as a river, lake, or bay. Urban watersheds are characterized by high impervious cover, engineered drainage networks, and significant human influence on the hydrologic cycle.
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